By the way, It just occurred to me that this might be important to mention. If the tip is useful, I recommend the OP add this info to his first post.
If you're building gnome-shell from source using jhbuild tools: You can keep the theme you're currently using (without having to re-do everything on updates) by committing your changes to your css file to git, like so.
This will open a changelog file in nano (terminal's text editor) that asks you for a breif commmit message.
$: cd ~/gnome-shell/source/gnome-shell
$: git commit -a
Just write something obvious like "CSS changes" where the cursor is (at the top where i wrote the same message) and press ctrl+o to save, enter to confirm and ctrl+x to quit.
Commit changes to the CSS file.
# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.
# Committer: Fernando Mora <fernando@homework.(none)>
# On branch master
# Your branch is ahead of 'origin/master' by 1 commit.
# Changes to be committed:
# (use "git reset HEAD <file>..." to unstage)
# modified: data/theme/gnome-shell.css
[ Read 14 lines ]
^G Get Help ^O WriteOut ^R Read File ^Y Prev Page ^K Cut Text ^C Cur Pos
^X Exit ^J Justify ^W Where Is ^V Next Page ^U UnCut Text^T To Spell
This will let any updates from git take place without bugging you about your weird CSS file, but i doubt it's foolproof. If you're daring, use
where X = number of commits to revert.